The goals of this application for continuation funding are: to deepen significantly our understanding of how a speaker's auditory acuity influences his or her speech motor planning; to describe the speech perception and production of hearing-impaired adults and the effects of cochlear prostheses; and to evaluate and help refine a quantitative model of the role of hearing in speech. We pursue these goals by conducting experiments with normal-hearing speakers, and with postlingually deafened adults who receive cochlear implants. Our experiments measure the effects of the implants on speech in recordings made before implantation and up to 2 years after, as speakers' auditory acuity evolves. According to our model of the role of hearing in adult speech motor control, many of the goals of speech movements are in the auditory domain. Consequently, a central theme of this research is the role of auditory perception in the feedback and feedforward control systems that are used to achieve auditory goals during speech. Feedforward control is almost entirely responsible for generating articulatory movements in adults. However, when there is a mismatch between the speaker's intention and the resulting auditory feedback during production of a speech sound, that error leads to corrective motor commands that serve to update feedforward commands for subsequent movements. The speaker's ability to detect such a mismatch depends on his or her auditory acuity. The proposed research inquires into the role of auditory acuity when producing phoneme and lexical stress contrasts; when compensating for feedback perturbation of vowel formants or for mechanical perturbation of sibilant spectra; and when imitating synthesized vowels. To measure acuity, we present synthetic speech continuation for discrimination testing. To assess relations with acuity, we measure the degree of separation of contrastive phonemes and lexical stress; dispersion of productions around their phoneme means; compensation for formant shift and for mechanical perturbation of sibilant spectra; and imitation accuracy. In most of these experiments, we also block auditory feedback temporarily in order to reveal the state of feedforward commands. Analyses take demographic variables such as age at hearing loss and duration of implant use into account. Relevance to public health: Hearing oneself speak plays a 2-fold role in maintaining good speech-it may correct the pronunciation of speech sounds even as they are occurring and it can revise plans for producing the sound next time. When a speaker is seriously hearing-impaired, those 2 mechanisms do not function well and speech can deteriorate over time. This project studies the idea that the people most affected are those who cannot distinguish the different speech sounds well. The results can serve to stimulate research on new therapies in which certain speech disorders, including those of speech development, are alleviated by training clients to hear differences better among the sounds that they produce. [unreadable] [unreadable] [unreadable]